The normal function of the nervous system is intimately related to the chemistry of its component parts--the neurons and glia. The communication of coded information between neurons relates to a specific component of this chemistry consisting of neurotransmitter substances and the enzymes associated with their synthesis and degradation. Only a few of the neurotransmitter substances are fairly well established, including acetylcholine, several catecholamines and serotonin, several amino acids, and some peptides. As would be expected, imbalances in any of these neurotransmitter systems can lead to serious malfunctions in the nervous system, and thus, in sensation, movement, or other behavior. This proposal constitutes a step in a long-range effort to understand the synaptic chemistry of structures related to visual function. The previous grant project emphasized the cholinergic system and the retina, with a beginning into examining the superior colliculus and the retinotectal projection. The present proposal emphasizes the inputs into the superior colliculus and expands the neurotransmitter systems studied to include enzymes related to excitatory and inhibitory amino acids (glutamate and aspartate/aspartate aminotransferase and glutaminase; Gamma-aminobutyric acid/glutamic acid decarboxylase) in addition to the enzymes of the cholinergic system (choline acetyltransferase and acetylcholinesterase). The present proposal also begins examining the cerebellum particularly the portion related to vestibular input (flocculonodular lobe) related to the vestibulo-ocular reflex. It is intended to obtain chemical data at such a resolution as to readily permit correlations with the considerable anatomical and physiological data available for these structures. This can be done via the methods of quantitative histochemistry, by which quantitative chemical data can be obtained for pieces of tissue as small as 20 Mum in linear dimension. The locations of these tissue samples can be recorded to provide a chemicl map comparable to anatomical or physiological maps. Quantitative changes in transmitter systems subsequent to lesions distrupting pathways into the superior colliculus or cerebellum will give indications of the relative associations of these systmes to particular inputs. The superior colliculus and the cerebellum serve as integration centers for visual, auditory, somatosensory, and vestibular input in the generation of eye movements. More information about the roles of neurotransmitters in normal visual processing will help in understanding possible malfunctions of these systems in visual disorders.